A SCUBA (Self Contained Underwater Breathing Apparatus) diver must adjust his or her overall buoyancy to maintain generally neutral buoyancy. In order to be approximately neutrally buoyant, a diver may have ballast weights as part of his or her equipment. Further, a diver may also control the amount of air in his or her lungs as a means for making fine adjustments for achieving neutral buoyancy or for causing a small descent or ascent. A Buoyancy Control Device (BCD) is used by a diver, generally, to make significant adjustments to maintain neutral buoyancy as the diver changes depth. Although water density does not change significantly with depth, water pressure increases by approximately one atmosphere (roughly 14.6 lbs/in2) for every 33 feet of depth. Air (and other gasses) responds to pressure and depth differently than liquids such as water. While fluids like water are essentially incompressible, gasses such as air are governed by Boyle's gas laws. Thus, when the pressure of a fixed mass of air in a flexible walled container is doubled, the volume of that air will be reduced by half. Prior art buoyancy control devices (BCDs) generally include a vest suitable for wearing by a SCUBA diver and the vest typically includes at least one air chamber and usually a set of air chambers having semi-flexible walls. In a prior art buoyancy control device (BCD), the diver, by means of a hand operated BCD valve, manipulates the valve between a normally closed condition in which air neither enters or leaves the BCD vest air chambers and two operational modes, namely: (1) a first mode in which air from a high pressure source (namely, a SCUBA air tank first stage regulator) flows into the BCD vest air chambers and (2) a second mode in which air is allowed to escape (valve off) from the BCD vest air chambers into the surrounding water. By manipulating such a prior art BCD valve, a skilled SCUBA diver is able to maintain near neutral buoyancy even while descending or ascending in the water column. This is accomplished, essentially, by keeping the volume of the air in the BCD vest air chambers generally constant (and thus the overall buoyancy of the diver and the diver's equipment generally constant) even as the pressure of that air in the vest air chambers varies greatly as the diver descends and ascends in the water column.
The manipulation of a present BCD is a skill that must be mastered by an aspiring SCUBA diver. To dive safely, a SCUBA diver, even when changing depth, must maintain an average buoyancy for himself or herself and his or her equipment (when considered together) that does not deviate significantly from a neutrally buoyant condition. As a diver descends, the pressure surrounding the air chambers of the BCD vest increases which causes the vest air chambers to decrease in volume. This decrease in volume decreases the amount of water being displaced by the diver and increases the average density of the diver and the diver's equipment. As this happens, the density of the surrounding incompressible water, does not change significantly with increasing depth. This decreases the buoyancy of the diver, resulting in a downward force that tends to increase the diver's rate of descent, which, in turn, causes the diver's buoyancy to decrease even faster. Accordingly, as the diver descends, the diver must constantly add air to the BCD air chambers to maintain their volume as depth increases in order to maintain neutral buoyancy. A reverse process occurs when the diver ascends. As the diver ascends, hydrostatic pressure surrounding the BCD vest air chambers decreases which allows the BCD air chambers to expand. When this happens, the water displaced by the diver increases as the average density of the diver including the diver's equipment decreases. Such an increase in displacement as the diver ascends causes the rate of ascent to increase resulting in a potentially dangerous runaway “buoyant ascent”. Thus, during an ascent, the diver must constantly manipulate a prior art BCD valve to vent air from the BCD vest air chambers in order to maintain the BCD air chambers at a constant volume to maintain neutral buoyancy. During a scuba dive, a diver must continually and actively maintain neutral buoyancy when using a prior art BCD. What is needed is a buoyancy compensation apparatus that automatically traffics air into and out of the BCD vest air chambers to maintain generally neutral buoyancy.